Text-based electronic communications such as e-mail messages, text messages, instant messages, facsimiles and the like are now in wide use around the world. As the use of such text-based electronic communications has increased, so has its misuse. One such misuse is the transmission of very large numbers of unsolicited electronic messages over the communications network. Such unsolicited bulk messages are typically referred to as electronic spam or “spam” for short, and the individuals or entities that transmit spam are often referred to as “spammers.” Transmitting electronic spam may be a relatively low cost operation for the spammer, as they may need only obtain and manage lists of electronic addresses such as e-mail addresses, Short Message Service (“SMS”) addresses, etc. to which the spam messages will be sent and, for some types of spam such as SMS spam, maintain one or more valid user accounts that the spam will be sent from. In contrast, spam may impose significant costs on the communication network provider(s) (internet service providers; cellular telephone operators, etc.), as they must ensure that the network has sufficient communications capacity to timely deliver all of the messages transmitted by network users/subscribers, including large volumes of spam. While the communications network providers presumably pass these costs along to subscribers, only a very small percentage of the subscribers are spammers, and hence the non-spammer subscribers bear almost all of the costs that spam imposes on the network provider. Most often spam is used for advertising purposes, but it also may be used for more nefarious purposes including, for example, as a means for tricking recipients into sending money or disclosing confidential information, or for tricking recipients into subscribing for premium services. In addition, spam may also be used for malicious purposes such as propagating electronic viruses and/or as a means of gaining control of the electronic devices that receive the spam and/or of gaining access to content such as passwords, account numbers, credit card information, etc. that is stored on such electronic devices.
Spam is also problematic because the vast majority of spam recipients find it annoying. Moreover, reviewing messages to determine which are spam and which deserve attention is time-consuming, and also may be error prone such that spam recipients may inadvertently delete, ignore or overlook legitimate messages believing that they are spam. Moreover, for some forms of text-based electronic communications, recipients of the communication may be charged on a per message basis. For these types of communications, spam may force subscribers to pay for messages that they did not ask to receive and which they do not want to receive. Thus, spam may result in dissatisfied subscribers, complaints that must be handled by customer service centers and other negative consequences for the communication network provider. Additionally, in some cases electronic spammers may take control of the electronic devices of others to transmit the spam messages, thus making it much more difficult to identify the real source of the spam (and perhaps incurring charges on the account of the electronic device that was “hijacked” by the spammer). While various efforts have been made by legislative bodies (i.e., laws making it illegal to send spam messages) and by communication network providers to control and reduce the amount of spam, the problem of spam continues to get worse over time as spammers use more sophisticated spamming techniques.